OPTIMAS: Overwrite Purging Through In-Execution Memory Address Snooping to Improve Lifetime of NVM-Based Scratchpad Memories

SRAM-based scratchpad memories (SPMs) used in embedded systems impose high leakage power. Designing SPMs based on non-volatile memories (NVMs) were proposed as NVMs have negligible leakage power. The main problem of utilizing NVMs across the SPM is their limited number of write cycles (endurance). This problem threatens the reliability of NVM-based SPMs. To alleviate the problem of limited endurance in NVM-based SPMs, this paper proposes a method, called overwrite purging through in-execution memory address snooping (OPTIMAS). The main idea behind the proposed method is to control the lifetime of NVM-based SPMs, directly by a hardware unit, outside of the SPM mapping algorithm. This idea enables the possibility of using traditional SRAM-based mapping algorithms in NVM-based SPMs. OPTIMAS controls the wear-out of NVM-based SPMs based on the recent write behavior of each block during the runtime of the programs. OPTIMAS is evaluated from the lifetime, energy consumption, and performance point of views. The simulation results show up to two orders of magnitude improvement in lifetime, an average of 50% reduction in dynamic energy consumption, and negligible performance overhead (less than 1%). Furthermore, it is shown that while OPTIMAS is orthogonal to all other approaches, it benefits from significant lifetime improvement in comparison with the state-of-the-art approaches.